Grain boundary enhanced UN and U
A method of forming a water resistant boundary on a fissile material for use in a water cooled nuclear reactor is described. The method comprises mixing a powdered fissile material selected from the group consisting of UN and U 3 Si 2 with an additive selected from oxidation resistant materials having a melting or softening point lower than the sintering temperature of the fissile material, pressing the mixed fissile and additive materials into a pellet, sintering the pellet to a temperature greater than the melting point of the additive. Alternatively, if the melting point of the oxidation resistant particles is greater than the sintering temperature of UN or U 3 Si 2 , then the oxidation resistant particles can have a particle size distribution less than that of the UN or U 3 Si 2 .
1. A nuclear fuel comprising:
a pellet comprised of compressed and densified grains of a fissile material selected from the group consisting of UN and U 3 Si 2 , the grains having grain boundaries; and
an oxidation resistant additive coating at least a portion of the grain boundaries of the fissile material;
wherein the additive has a melting point greater than the sintering temperature of the fissile material, the additive is melted into at least a portion of the grain boundaries, and the additive has a median particle size less than that of UN or U 3 Si 2 .
2. The nuclear fuel recited in claim 1 wherein the fissile material is UN, and the additive is selected from the group consisting of tungsten and alloys containing at least 50 atomic % thereof, and UO 2 .
3. The nuclear fuel recited in claim 1 wherein the additive is present in amounts less than 20 weight percent of the fissile material.
4. The nuclear fuel recited in claim 1 wherein the median particle size of the additive is less than 10% of the median particle size of the UN or U 3 Si 2 .
5. The nuclear fuel recited in claim 1 wherein the median particle size of the additive is less than 1% of the median particle size of the UN or U 3 Si 2 .
6. The nuclear fuel recited in claim 1 wherein the powdered fissile material is U 3 Si 2 , and the additive is selected from the group consisting of molybdenum, titanium, chromium, thorium, tungsten, niobium, and zirconium, alloys containing at least 50 atomic % thereof, BeO, and UO 2 .
7. A nuclear fuel comprising:
a pellet comprised of compressed and densified grains of a fissile material UN, the grains having grain boundaries; and
an oxidation resistant additive coating at least a portion of the grain boundaries of the fissile material;
wherein the additive has a melting point lower than the sintering temperature of the fissile material, the additive is melted into at least a portion of the grain boundaries, and the additive is a borosilicate glass.
8. The nuclear fuel recited in claim 7 wherein the additive is present in amounts less than 20 weight percent of the fissile material.
9. A nuclear fuel comprising:
a pellet comprised of compressed and densified grains of a fissile material U 3 Si 2 , the grains having grain boundaries; and
an oxidation resistant additive coating at least a portion of the grain boundaries of the fissile material;
wherein the additive has a melting point lower than the sintering temperature of the fissile material, the additive is melted into at least a portion of the grain boundaries, and the additive is a borosilicate glass.
10. The nuclear fuel recited in claim 9 wherein the additive is present in amounts less than 20 weight percent of the fissile material.